1. Field of the Invention
This invention relates to a method of manufacturing an anode assembly of a magnetron used in a microwave oven, which is usually referred to as an electronic range, to generate an electromagnetic wave for cooking foodstuffs therein, and in particular a method of manufacturing such an anode assembly by assembling vanes, an antenna lead, upper and lower strip rings and an anode cylinder together.
2. Description of the Prior Art
Generally, a magnetron is of a type as shown in FIG. 1 of the accompanying drawings and is a kind of a diode comprising a direct-heated filament (referred to as a cathode) (1) disposed axially at its central position and an anode cylinder (referred to as an anode) (2) which is an anode structure mounted in a radially outwardly spaced, surrounding relation to the cathode. In addition, the magnetron is provided with a magnetic circuit comprising a yoke(3), a magnet(4) and a magnetic pole(5) and applying magnetic flux into a space between the filament(1) and the anode cylinder(2), an output section comprising an antenna lead(6), an antenna seal(7), an antenna ceramics(8) and an antenna cap(9) and emitting microwave energy transferred to the anode cylinder(2) to the exterior of the magnetron, radiatin fins(11) for radiating heat generated due to collision of thermions with vanes(10) in the anode cylinder(2), and a filter circuit for preventing an unnecessary high frequency component produced in an action space from back-flowing to a power source.
In such a magnetron, the thermions emitted from the filament(1) effect a cycloidal movement as they are subject to the force of an electric field induced between the vanes(10) and the filament(1) and the magnetic flux applied into the space between the filament(1) and the anode cylinder(2) by the magnetic pole(5) of the magnetic circuit. The accelerated thermions generate the microwave energy which will be received by the vanes is emitted through the antenna lead(6) of the output section to the exterior of the magnetron to heat the foodstuffs placed within the microwave oven. In particular, there is mounted in a radially outwardly spaced, surrounding relation to the filament or the cathode an assembly generically referred to as an anode assembly comprised of the anode cylinder(2) of a circular cross-sectional configuration, a plurality of the vanes(10) arranged radially within the anode cylinder(2), upper and lower strip rings(12,13), each engaged with each of the upper and lower sides of the radially arranged vanes (10), and the antenna lead(6) coupled to one of the vanes, as shown in FIG. 2.
As will be described below with reference to FIGS. 3 and 4, a prior method of manufacturing the anode assembly as described above comprises the steps of:
(a) providing a plurality of rectangular plate vanes(10), each having upper and lower ring-receiving grooves(10b,10a) formed in its upper and lower sides, one of the vanes having a lead-receiving groove(10c) formed at an approximately central portion of its upper side,
(b) forming a lower strip ring having inner and outer ring portions(12a, 12b) to be inserted into the lower grooves(10a) of the vanes (10), and then plating the ring portions with a brazing material,
(c) making an anode cylinder(2) of a circular cross-sectional configuration by cutting a pipe or bending a sheet into a cylindrical member and precisely finishing it,
(d) placing the lower strip ring having the inner and outer ring portions(12a,12b) formed in the Step(b) and the anode cylinder(2) made in the Step(c) on a base jig(20) having a plurality of circumferentially spaced longitudinal grooves(20a),
(e) inserting the respective vanes(10) prepared in the Step(a) into the respective longitudinal grooves(20a) of the base jig(20),
(f) fitting an antenna lead(6) with a brazing material(15) connected to its lower end as shown in FIG. 4, into the groove(10c) of one of the vanes formed in the Step(a),
(g) then, assembling in sequence a center pin jig(21), an upper strip ring having inner and outer ring portions(13a, 13b) coated with a brazing material in the same manner as the Step(b), and an upper jig(22) having a plurality of circumferentially spaced longitudinal slots(22a) formed in its peripheral wall,
(h) inserting cut brazing wires(16) of given length through each slots(22a) of the upper jig(22) toward the vanes(10), and
(i) passing the so obtained assembly through a heating furnace having a sufficient temperature, for example, of about 800.degree. C.-about 950.degree. C., to melt the brazing materials, thereby enabling the components of the assembly to be joined to each other by the molten brazing materials.
In this process, the contact surfaces between the components are joined to each other by the molten brazing material flowing into between them. More particularly, the vanes(10) are bonded to the inner wall of the anode cylinder(2) by the melt of the brazing wires(16) flowing into between them through the slots(22a) of the upper jig(22), the antenna lead(6) is bonded at its lower end to the vane(10) by the brazing material(15) attached to the lower end, and the inner and outer ring portions(12a, 12b, 13a, 13b) of the lower and upper strip rings are joined to the vanes(10) by the brazing material coated on outer surfaces of the strip rings. At this time, since the jigs, such as the base jig(20), the center pin jig(21) and the upper jig(22), used in the assembling operation are made of the material of a low thermal expansion coefficient, such as carbon or tungsten oxide, which may not be bonded to the brazing materials, joining of the jigs to the adjacent components by the brazing materials does not occur even during the heat treatment.
The prior art of manufacturing the anode assembly by the process as described above, is however disadvantageous in that the manufacturing process is tedious and time-consuming and requires higher manufacturing cost because it needs the steps of cutting the brazing material into the wires of given size used to join the vanes to the inner wall of the anode cylinder and vertically inserting the respective wires through the respective slots formed in the outer periphery of the upper jig. Such a complicated operation also results in lower productivity. Furthermore, possible incomplete insertion of the brazing materials into the given sites during the assembling operation leads to an increase of a defective. In addition, this prior method has lower productive efficiency and higher fraction defective, which result from the complicated operation of forming in advance the brazing material used for joining the antenna lead to the vane by means of a mold and a forming apparatus, and then fixing the formed brazing material to the lower end of the antennal lead.